The present invention relates to tools used in the machining of materials by machine tools. More particularly, the invention provides a rotary end mill for the rough and fine machining of metals, a drill particularly suited to the drilling of deep holes, and a reamer also for machine use.
End mills are widely used in milling operations due to their versatile range of application and due to the moderate first cost of the tool. Integral end mills are often of cylindrical shape, and are available up to about 80 mm diameter, Many end mills have flat ends; although other shapes such as conical and rounded ends are also used. An end-mill typically has 2 to 10 teeth, depending on diameter, size and whether intended for rough cutting or finishing. Teeth are usually of spiral shape, but can be straight parallel to the axis. Teeth are also provided at the end face. End mills have a shank portion and a cutting portion, although some end mills have a cutting portion at each side of the shank portion. Material of construction is high speed steel, solid carbide, Wolfram carbide, Cubic boron nitride, Poly-crystal diamond, cermets, ceramic, and combinations thereof. Coatings are often applied to the cutter to extend the working life thereof.
The design of an end mill is a function of the balance between contradictory requirements—rigidity to prevent tool chatter and strength to avoid breakage, versus generous spacing between the teeth to allow the clearance of chips and access for a liquid coolant. With regard to drills similar considerations apply, when the depth of the hole being drilled is several times as large as the diameter of the drill.
In conventional end mills the shape and thickness of the tooth, determined with reference to the expected use of the cutter, remains constant along the length of the cutting tool. An improvement on the constant cross-sectional shape and size of a milling cutter was disclosed in a previous patent, U.S. Pat. No. 6,742,968 dated Jun. 1, 2004. The cutter tool disclosed was an end mill wherein the total cross-sectional area of the cutter material and particularly the core portion, taken at right angles to the cutter axis, increases gradually from the cutting end towards the cutter shank. This design provided a cutter which combined adequate chip clearance with improved rigidity.
With regard to drills intended for the drilling of deep holes, the difficulty of chip clearance and application of a coolant to the cutting tip of the drill is more severe than with end mills, and often there is little choice but to withdraw the drill at least once during the drilling of a single hole. Failure to do so may result in the spaces between the spirals being jammed with chips and the drill being broken or damaged by overheating due to coolant being unable to reach the drill tip.
Similar conditions apply to machine reamers, although the small quantity of removed metal causes little difficulty.
The machining of features such as slots, flats, outer profile, gear teeth and the like is often executed in three stages—rough machining with maximum possible metal removal rates, machining to near dimensions and finish machining to produce a smooth surface. Often different cutting tools are needed for each stage of machining, the changeover causing lost time and resetting. This could be avoided if a multi-purpose tool were available to carry out the whole machining process.